Integrated circuits which use the light sensing properties of a silicon junction to detect the ambient light and to switch a flashing incandescent lamp powered from a battery power supply in accordance with the ambient light level are known. Integrated circuits incorporating such a junction, along with circuitry to intermittently power the lamp while a given level of ambient light is detected are available. External to the chip, networks of resistors and capacitors provide necessary time constants to control the flash rate of the light. These RC time constants set the ON and OFF time period of each flash cycle.
Later developments incorporated the timing circuits into the chip using an internal oscillator, compensated for temperature and component spreads, with a digital frequency divider to offer the required output period and frequency.
It has been found that ambient light generates leakage currents in reverse biased junctions (and photo-voltaic voltages in a unbiased junctions), so the design of these integrated circuits has needed to take into account the inherent characteristics of the silicon circuit and by appropriate layout or other means, to ensure that any incident light does not produce unexpected light induced signals and cause the circuit to exhibit unintended behaviour.
Known barricade warning lamps have a light source placed at the focus of on optical system adapted to condition the light output into a beam with desired directional characteristics. This system may include focusing lenses and reflectors.
While a light source occupies the central position at the focus of the lens system for these known barricade warning lamps, it has been found that the optimum position for the location of a light sensor is also near to this focus to offer a best sensitivity to ambient light. Of course it is better to isolate the sensor from the light source, to prevent the light from the lamp disrupting the detection of the ambient light. This gives rise, however, to the problem that the sensor and the light source would then need to occupy the same space but be visually isolated from each other.
A further problem is that it is expensive to encapsulate a control integrated circuit in a manner that also allows it to sense the ambient light, or alternatively to provide a diode or light sensitive transistor in a separate transparent package.
It is also known to have a lamp operate in a continuous mode in which the lamp is on apparently continuously at any time the light sensor registers darkness. If light is detected the lamp is turned off to check on the true ambient light level, and if it is found to be still dark (the detected light having been being the lamp light falling on the sensing area) the lamp is immediately switched back on, the process repeating at short intervals. While this does involve a brief break in the lamp illumination, in practice it can be so brief as to not be noticeable.
Recent developments in light emitting diode technology has enabled a filament lamp to be replaced by light-emitting diodes. With a barricade flasher then which has an output directed in two oppositely directed paths there can be one diode at each focus of the plastic lenses of the lamp. Each light-emitting diode is directed in the direction of the beam of the lens, giving a pair of light-emitting diodes mounted in opposing directions back to back at the focus of the lamp lenses.
It is an object of this invention to provide means to overcome one or more of the disadvantages of the prior art, or at least to provide the public with a useful alternative.